1. Field of the Invention
This invention relates to a printed circuit board and an electronic device for connections between circuits in a personal computer and office automation devices.
This application is based on Japanese Patent Application No. 10-229138, the contents of which are incorporated herein by reference.
2. Background Art Including Information Disclosed Under37 CFR 1.97 and 1.98
In general, office automation devices such as personal computers and workstations include a number of printed circuit boards. As demand for acceleration of data processing and reduction in size has recently increased, the clock frequencies in the circuits have increased to more than several 100 MHz.
As the clock frequencies increased, however, unnecessary radiant noise may occur in the circuits on the printed circuit board. Because of the increase of the clock frequencies, the differences in length between connection lines may change the inductance. As the result, input signals show waveforms which include ringing, as shown in FIG. 3 (with the overshoot to 9V and the undershoot to -7V), which leads to the occurrence of unnecessary radiant noise. Further, when the terminating resistances change due to the irregularity of manufactured transmission lines, the characteristics of the impedance may be unbalanced, ringing may occur in the waveforms, and reflection of signals may occur, causing a malfunction or destruction of the semiconductor device.
Japanese Unexamined Patent Application, First Publication No. Hei 4-97562 discloses a technique for adjusting terminating resistances to suppress ringing in waveforms by selecting one of a number of terminating resistances. Japanese Unexamined Patent Application, First Publication No. Hei 6-152355 discloses a technique to suppress the ringing by a dummy line whose one end is open or connected to the ground. Japanese Unexamined Patent Application, First Publication No. Hei 6-177612 discloses a technique to manufacture a printed circuit board of a material which can suppress the ringing.